I'll post exact details in a few hours, but essentially i got a boots artifact with +10 spd, +5 search, from a minor unique at DL30 circa.
Was i just very lucky? Because there is no way this unique would have dropped ego speed +10 at this depth. Is the power level of artifacts calculated differently than that of egos?

The power level of artifacts is set independently of their native depth and frequency. Hence why e.g. Thorin tends to show up early; it's disproportionately good for the depth at which you normally find it, but that's just how it's set in the files. Randarts aim for a similar distribution of power vs. depth/rarity as standarts, so it's not unreasonable to have sudden spikes in power.

+10 speed at dlvl30 is pretty unusual, even considering what I just said. Boots/rings of speed have been found earlier, though. It's very rare, but not 100% impossible.

I think the winner for "rarest event" in my memory was someone who managed to find the One Ring before making it to dlvl20. As I recall they shared the savefile on Usenet so other people could experience playing almost an entire game with the One.

So, if standarts (about time we added this word to the forum's spellchecker) have a power AND a native depth, which may not be directly related, how do randards do that? How does the game know that random artifact of power 247 needs DL41 native, and random artifact of power 258 needs native DL52?

what if ...

we pooled everything in one big list. artifacts and egos, and standard gear too. order by power. (egos will need an "average" power as the actual stats can vary)

and then whenever you kill a mob, it has "drop item 1d(power)"

no need to differentiate between normal, good and great. Also makes more sense to want to chase down big mobs.

i love these because they are sandals, so they weight very, very little ...